Recirculating combustion apparatus jet pump

ABSTRACT

A combustion apparatus for a gas turbine engine includes a Coanda effect jet pump by which air introduced for combustion recirculates combustion products into the combustion zone of the apparatus. The jet pump is effective to improve the recirculation ratio while maintaining an acceptably low pressure drop in the combustion apparatus. The combustion air flows through the interior of the body of the Coanda nozzle and over a wall which terminates in a lip converging toward the radial surface of the Coanda nozzle body. A guiding surface at the end of the lip improves flow into the nozzle. Vanes or struts extending across the nozzle preserve alignment of the body and lip.

nited States Patent [19] Sherman et a1.

[ Dec. 3, 1974 1 RECIRCULATING COMBUSTION APPARATUS JET PUMP [75]Inventors: Warren S. Sherman; Albert J.

Verdouw, both of Indianapolis, Ind.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: July 2, 1973 [21] Appl. No.: 375,538

[52] US. Cl 60/39.65, 60/DIG. 11, 417/196,

4l7/197,417/198,431/116 [51] Int. Cl. F026 3/00 [58] Field of Search60/3952, 269, 271, 231,

60/3965; 417/196-198, 171, 151; 239/DIG. 7, 265.17; 137/803; 431/116;244/42 .CD

[56] References Cited UNITED STATES PATENTS 2,052,869 9/1936 Coanda239/DIG. 7 2,108,652 2/1938 Coanda 4l5/DIG. 1

3,062,483 11/1962 Davidson 239/DIG. 7 3,319,692 5/1967 Reba et al....431/116 3,321,891 5/1967 Coanda.... 417/196 3,337,121 8/1967 Coanda60/264 X 3,589,383 6/1971 Garnier 417/198 3,744,242 7/1973 Stettler etal. (SO/DIG. 11

FOREIGN PATENTS OR APPLICATIONS 1,930,809 6/1969 Germany 415/D1G. 1

OTHER PUBLICATIONS Reba, 1., Applications of the Coanda Effect,Scientific American, June, 1966, pp. 84-90.

Primary Examiner-Carlton R. Croyle Assistant Examiner-Robert E. GarrettAttorney, Agent, or FirmPaul Fitzpatrick 57 ABSTRACT A combustionapparatus for a gas turbine engine includes a Coanda effect jet pump bywhich air introduced for combustion recirculates combustion productsinto the combustion zone of the apparatus. The jet pump is effective toimprove the recirculation ratio while maintaining an acceptably lowpressure drop in the combustion apparatus. The combustion air flowsthrough the interior of the body of the Coanda nozzle and over a wallwhich terminates in a lip converging toward the radial surface of theCoanda nozzle body.

A guiding surface at the end of the lip improves flow into the nozzle.Vanes or struts extending across the nozzle preserve alignment of thebody and lip.

4 Claims, 4 Drawing Figures RECIRCULATING COMBUSTION APPARATUS JET PUMPOur invention is directed to combustion apparatus, particularly such asoperates at substantially superatmospheric pressure; it is moreparticularly directed to an improved jet pump in such combustionapparatus for causing recirculation of combustion products from theoutlet to the inlet of a zone in which combustion takes place. 1

Reba et al US. Pat. No. 3,319,692, May 16, 1967,

teaches recirculation of combustion products in an oil burner by aCoanda-type pump to obtain more complete combustion and thus minimizeunburned hydrocarbons, carbon monoxide, and smoke.

Recirculation has also been proposed as a means to reduce nitrogenoxides generated in the combustion apparatus by the reaction of nitrogenand oxygen from the atmosphere in a high temperature combustion zone.The amount of nitrogen oxide generated increases with increasedtemperature and with increasing concentration of oxygen in thecombustion zone; also, with time of residence in the hot zone. Byrecirculating combustion products, the concentration of oxygen in thecombustion zone may be lowered and also the temperature may belowered tosome extent. This concept is described in the copending applications ofStettler and Verdouw, Ser. No. 202, 191 filed Nov. 26, 1971 forCombustion System and Ser. No. 220,607 filed Jan. 25, 1972 forRecirculating Combustor, US. Pat. No. 3,744,242, both of commonownership with this application.

Our present invention may be regarded primarily as an improvement on thecombustion apparatus of Ser. No. 220,607, the improvement residing in amore efficient and effective Coanda effect jet pumping structure forrecirculating the combustion products.

To minimize nitrogen oxides a relatively high recirculation ratio isdesired, of the order of one to two. The recirculation ratio is theratio of flow per unit time of recirculated combustion productsto flowof primary combustion air entering the combustion apparatus. This is tobe distinguished from dilution air which is mixed with the combustionproducts at the termination of combustion. It is important to effect therecirculation with a minimum of pressure loss in the combustionapparatus, because pressure drops in the combustion apparatus detractfrom the efficiency of the gas turbine engine. It is also desirable thatthe recirculation ratio ramain substantially constant over a wide rangeof flow rates as the output of the combustion chamber is varied to varyengine power output.

The combustion apparatus described in Ser. No. 220,607 includes a jetpump of the Coanda type disposed near the downstream end ofthecombustion zone of the combustion apparatus to introduce the freshcombustion air and entrain with it combustion products which arerecirculated into the upstream end of the combustion apparatus.

The principal object of our present invention is to provide an apparatusof the type described in Ser. No. 220,607 which is more efficient andbetter meets the requirements of practice. It is a further object toprovide a jet pump for such an installation which has better efficiencythan those previously known.

The nature of our invention and its advantages will be apparent to thoseskilled in the art from the succeeding detailed description of thepreferred embodiment of i the invention and the accompanying drawings.

FIG. 1 is a schematic illustration of a gas turbine.

combustion apparatus in axial sectional view.

FIG. 2 is an enlarged structural view of the jet pump portion of thecombustion apparatus.

FIG. 3 is a fragmentary sectional view taken on the plane indicated bythe line 3-3 in FIG. 2.

FIG. 4 is an enlarged diagrammatic illustration of the jet pump nozzleconfiguration.

FIG. 1 illustrates a combustion apparatus 2, which preferably is ofcircular cross section. The apparatus includes an outermost wall 3 whichextends from an inlet 4 for combustion air substantially to an outlet 6for combustion products from the combustion apparatus. An innermost wall7 defines a combustion zone 8 having an upstream end at 10 and adownstream end at 11. At its upstream end the wall 7 is connected by atoroidal manifold 12 to an inner wall 14 generally surrounding theinnermost wall 7. Manifold 12 is connected by a number of spacedcombustion air tubes 15 (six as shown) to a forward wall 16 disposednear the air inlet 4. I

The forward wall connects tubes 15 to an outer wall 18 lying closelywithin the outermost wall 3. Wall 18 is supported from wall 3 by meanswhich need not be described. Wall 18 converges into a discharge portion19 extending into the outlet 6 and which defines a dilution zone 20.Some of the air introduced through inlet 4 flows through the annularpassage 22 between walls 3 and 18 and through holes 23 into the dilutionzone. Additional air may flow through smaller openings as indicated bythe arrows at 24. If desired, means may be provided for varying thequantity of dilution air, indicated schematically as a rotatable ring 26having openings 27 variably registrable with the holes 23 in the wall18.

The primary combustion air flows from the inlet 4 through tubes 15 intomanifold 12 and then through a primary air passage 28 between walls 7and 14 to a Coanda nozzle type jet pump 30. The pump includes a body 31defined by the incurved downstream end of wall 14 and a lip 32 definedby the outcurved downstream end of wall 7. Primary air dischargedthrough the nozzle 34 between the body and lipflows upstream through therecirculation passage 35 defined between walls 14 and 18 and then,asindicated by the arrow 36, between tubes 15 into the combustion zone8. Fuel is introduced through a nozzle 38 supplied from any suitablesource and is ignited by suitablemeans (not illustrated). Combustionproducts flow through the outlet at the downstream end 11 of thecombustion zone. As indicated by arrow 39, a portion of these combustionproducts are entrained and pumped by the flow from jet nozzle 34 intothe recirculating passage. Preferably, approximately one to two times asmuch combustion products are recirculated as the flow of primarycombustion air through duct 28. The remainder of the combustion productsflow to the dilution zone 20 where additional air is mixed with them,and the resulting mixture is discharged through the outlet 6.

Except for the difference in the Coanda nozzle structure and therepresentation of control of dilution air, the structure described aboveis essentially the same as that described in structural detail in US.Pat. No. 3,744,242, and there is no need to enlarge upon details of thisstructure to understand the present invention.

Referring now to FIGS. 2 and 3, the structure and proportions of theCoanda nozzle and associated structure are more fully described. FIG. 2illustrates the downstream end of the major portion of walls 7 and 14,which are kept properly spaced by fins 40 fixed to wall 7. These wallsterminate in joining strips 41 and 42, respectively, welded to thewalls. The main wall 14 has a butt joint with a terminal portion 43which includes a flange strip 44 which receives the edge of strip 41.The two parts of the wall are tack-welded together as indicated at 45.

The innermost wall 7 has a continuing converging portion 46 which issimilarly joined to the innermost wall 7 at the tack weld 47. The wall14 terminates in a roughly quarter-circular cross section ring 31 whichdefines the body of the Coanda nozzle. This ring is seamwelded at 50 toan inner ring 51 which defines a gradually converging outlet from thecombustion air passage 28 into the Coanda nozzle. The chamber betweenwalls 31 and 51 is ventilated through scallops 52 in the inner ring. Thelip 32 of the Coanda nozzle, which also defines the downstream end ofthe combustion zone, is a ring of the cross section illustrated, theforward surface of which defines one boundary of the jet nozzle 34. Lip32 is seam-welded at 54 to the portion 46 of the innermost wall.

To connect the body 31 and lip 32 and maintain accurate spacing of thesetwo so that the precise width of the jet nozzle 34 is maintained, thereare provided a number of rectangular plates or vanes 55 which aredisposed in notches in the outer margin of lip 32 and the inner marginof body 31. These vanes are simply small flat metallic plates which aretack-welded to the body and lip. Preferably, there are 16 of thesedistributed around the circumference. They extend radially from the axisof the combustor.

It will be noted that the lip 32 has a cylindrical outer surface 56,which we term a guiding surface, extending a suitable distance from thebody 31. This guiding surface, in comparison with structures in whichthe outer edge of the lip is relatively thin, improves the recirculationof combustion products.

It has been found experimentally that a narrow edge to lip 32 (a verysmall or zero width of surface 56) is not detrimental to the attachmentof the impelling flow from gap 34 to the surface of wall 31, but it isinimical to entrainment. Good entrainment begins to be obtained as theratio of width of guiding surface 56 to the width of the nozzle gapapproaches unity, and best resuits are obtained with a guiding surfacesomewhat wider than the nozzle gap.

Investigation of the flow employing a surface coated with oil andlampblack to visualize the flow indicated that the guiding surfacepromotes the formation of vortices adjacent gap 34, thereby increasingthe entrainment ratio. Thus the recirculation ratio may be increased, orthe pressure loss through the nozzle may be decreased, by the provisionof the guiding surface.

The preferred geometry of the jet nozzle as it appears to us from theresults of our experiments with the structure may be further explainedwith reference to FIG. 4. This is an enlarged fragmentary view of thebody 31 and lip 32. The line 58 in FIG. 4 is perpendicular to thesurface of the body at the plane of the nozzle or outlet 34, and line 59is tangent to the body at this point. Line 60 represents the directionof convergence of the inner surface of the lip 32, and line 62represents the direction of the guiding surface 56. The angle indicatedas A between lines 59 and represents the angle of convergence of the jetnozzle outlet and the angle indicated as B represents the divergence ofthe surface 56 from the perpendicular 58 to body 31. Preferably, in thelight of results obtained so far, the angle A should be of the order of35 and angle B of the order of 5. With angle A equal to 35, the angle ofconvergence of the center of the jet nozzle relative to body 31 is 17 Itmay also be defined as the angle between a surface equidistant from theboundaries (body 31 and lip 32) of the nozzle and the forward boundary(body 31) at the nozzle outlet.

When our combustion chamber is used in a gas turbine engine, which it isprimarily intended for, the airflow will vary quite widely, but there isa maximum airflow determined by the maximum capacity of the engine. Itis desired that the ratio of recirculated air to incoming combustion airremain relatively constant at the total airflow changes, and this hasbeen found to be the case with the recirculation structure illustrated.Since airflow is fixed by engine requirements, it is apparent that thepressure drop required to force the incoming combustion air through thenozzle 34 will be a function of its total area, which is fixed by itsdiameter and the width of the nozzle gap. The nozzle diameter is afunction of the allowable dimensions of the combustion chamber, whichare determined by various considerations. The gap may be readily variedto suit the requirements. As the gap is widened, the pressure drop ofcourse falls, but it has been found by experiment that the recirculationratio also drops. The design of such a device therefore should be aimedat the best balance between the desired recirculation ratio and pressuredrop.

We have found in practice that narrowing the gap 34 to the point atwhich the desired recirculation ratio is obtained in a typical combustorleads to undesirably high pressure drops, and our combustion apparatusinvolves a further feature to give flexibility in overcoming thisdifficulty. As shown in FIGS. 2 and 3, the forward edge of the body 31is spaced from the terminal portion 43 of the wall 14 around thecircumference of the combustion liner. lnwardly projecting ridges 63spaced around the forward edge of the body portion 31 engage theterminal portion 43 leaving a substantially annular air outlet 64between the two. Braze metal deposited in holes 66 in the ridges 63 mayfix these together, and an additional seam weld may be provided as shownat 67.

The result of this is that some of the primary combustion air flowingthrough passage 28 escapes through the outlet 64, flowing forwardly andmixing with the recirculated combustion products and propelling airpassing over the outer surface of wall 14. The outlet 64 is notprimarily intended as a jet pump, although it should have some effect inpumping the recirculating combustion products. The primary purpose is toreduce the pressure of the primary air and maintain the greatestefficiency of recirculation by the Coanda effect jet pump.

It has been found possible to attain a recirculation ratio of 2.5 with apressure drop of under 5 percent with an apparatus as illustrated. Thisis with an apparatus in which the diameter of the combustion zone isapproximately 8 kinches, the diameter of the jet nozzle is approximately7 74 inches, and its width l/l0 inch.

Such a combustion liner is of dimensions suitable for a small gasturbine engine of moderate pressure ratio.

Reference to a small acute angle in the appended claims is intended toinclude an angle of 0.

It should be apparent to those skilled in the art upon consideration ofthe foregoing that the apparatus described is very well adapted tofunction effectively as a combustion apparatus with substantialrecirculation.

The detailed description of the preferred embodiment of the inventionfor the purpose of explaining the principles thereof is not to beconsidered as limiting or restricting the invention, since manymodifications may be made by the exercise of skill in the art.

We claim:

1. A combustion apparatus comprising, in combination, an innermost walldefining a combustion zone having upstream and downstream ends, an innerwall defining an annular air passage with the innermost wall, an outerwall defining with the inner wall an annular recirculation passage fromthe downstream to the upstream end of the combustion zone and defining adischarge passage from the combustion zone, and an outermost walldefining a dilution air passage with the outer wall to conduct air intothe discharge passage; the downstream end of the inner wall being curved,inwardly to form a forward boundary for a Coanda nozzle, and thedownstream end of the innermost wall being curved outwardly to define arear boundary for the Coanda nozzle, the Coanda nozzle encircling thedownstream end of the combustion zone between the said curved endsadapted to discharge into the recirculation passage and entraincombustion products discharged from the combustion zone into therecirculation passage; comprising a structure in which the forwardboundary of the nozzle is substantially radial, the rear boundary of thenozzle converges toward the forward boundary to define a converging airentrance to the nozzle such that a surface equidistant from the saidboundaries is directed at an acute angle less than 30 to the forwardboundary at the nozzle outlet, and the rear boundry terminates in aguiding surface directed at a small acute angle to a perpendicular tothe adjacent forward boundary of the nozzle outlet, the guiding surfacehaving a width greater than the width of the nozzle outlet; and asupplementary outlet means from the said air passage into therecirculation passage bypassing the Coanda nozzle.

2. A combustion apparatus comprising, in combination, an innermost walldefining a combustion zone having upstream and downstream ends, an innerwall defining an annular air passage with the innermost wall, an outerwall defining with the inner wall an annular recirculation passage fromthe downstream to the up stream end of the combustion zone and defininga discharge passage from the combustion zone, and an outermost walldefining a dilution air passage with the outer wall to conduct air intothe discharge passage; the downstream end of the inner wall being curvedinwardly to form a forward boundary for a Coanda nozzle, and thedownstream end of the innermost wall being curved outwardly to define arear boundary for the Coanda nozzle, the Coanda nozzle encircling thedownstream end of the combustion zone between the said curved endsadapted to discharge into the recirculation passage and entraincombustion products discharged from the combustion zone into therecirculaat a small acute angle to a perpendicular to the adjacentforward boundary of the nozzle outlet, the guiding surface having awidth greater than the width of the nozzle outlet; and a supplementaryoutlet means from the said air passage into the recirculation passagebypassing the Coanda nozzle.

3. A combustion apparatus comprising, in combination,.an innermost walldefining a combustion zone having upstream and downstream ends, an innerwall defining an annular air passage with the innermost wall, an outerwall defining with the inner wall an annular recirculation passage fromthe downstream to the upstream end of the combustion zone and defining adischarge passage from the combustion zone, and an outermost walldefining a dilution air passage with the outer Wall to conduct air intothe discharge passage; the downstream end of the inner wall being curvedinwardly to form a forward boundary for a Coanda nozzle, and thedownstream end'of the innermost wall being curved outwardly to define arear boundary for the Coanda nozzle, the Coanda nozzle encircling thedownstream end of the combustion zone between the said curved endsadapted to discharge into the recircu- -tion passage; comprising astructure in which the forward boundary of the nozzle is substantiallyradial, the rear boundary of the nozzle converges toward the forwardboundary to define a converging air entrance to the nozzle such that asurface equidistant from the said boundaries is directed at an acuteangle less than 30 to the forward boundary at the nozzle outlet, and therear boundary terminates in a guiding surface directed at an angle lessthan 10 to a perpendicular to the adjacent forward boundary of thenozzle outlet, the guiding surface having a width greater than the widthof the nozzle outlet; and a supplementary outlet means from the said airpassage into the recirculation passage bypassing the Coanda nozzle.

4. A combustion apparatus comprising, in combination, an innermost walldefining a combustion zone having upstream and downstream ends, an innerwall defining an annular air passage with the innermost wall, an outerwall defining with the inner wall an annular recirculation passage fromthe downstream to the upstream endof the combustion zone and defining adischarge passage from the combustion zone, and an outermost walldefining a dilution air passage with the outer wall to conduct air intothe discharge passage; the downstream end of the inner wall being curvedinwardly to form a forward boundary for a Coanda nozzle, and thedownstream end of the innermost wall being curved outwardly to define arear boundary for the Coanda nozzle, the nozzle encircling thedownstream end of the combustion zone between the said sage; comprisinga structure in which the forward at an angle less than 10 to aperpendicular to the adjacent forward boundary of the nozzle outlet, theguiding surface having a width greater than the width of the nozzleoutlet; and a supplementary outlet means from the said air passage intothe recirculation passage bypassing the Coanda nozzle,

1. A combustion apparatus comprising, in combination, an innermost walldefining a combustion zone having upstream and downstream ends, an innerwall defining an annular air passage with the innermost wall, an outerwall defining with the inner wall an annular recirculation passage fromthe downstream to the upstream end of the combustion zone and defining adischarge passage from the combustion zone, and an outermost walldefining a dilution air passage with the outer wall to conduct air intothe discharge passage; the downstream end of the inner wall being curvedinwardly to form a forward boundary for a Coanda nozzle, and thedownstream end of the innermost wall being curved outwardly to define arear boundary for the Coanda nozzle, the Coanda nozzle encircling thedownstream end of the combustion zone between the said curved endsadapted to discharge into the recirculation passage and entraincombustion products discharged from the combustion zone into therecirculation passage; comprising a structure in which the forwardboundary of the nozzle is substantially radial, the rear boundary of thenozzle converges toward the forward boundary to define a converging airentrance to the nozzle such that a surface equidistant from the saidboundaries is directed at an acute angle less than 30* to the forwardboundary at the nozzle outlet, and the rear boundry terminates in aguiding surface directed at a small acute angle to a perpendicular tothe adjacent forward boundary of the nozzle outlet, the guiding surfacehaving a width greater than the width of the nozzle outlet; and asupplementary outlet means from the said air passage into therecirculation passage by-passing the Coanda nozzle.
 2. A combustionapparatus comprising, in combination, an innermost wall defining acombustion zone having upstream and downstream ends, an inner walldefining an annular air passage with the innermost wall, an outer walldefining with the inner wall an annular recirculation passage from thedownstream to the upstream end of the combustion zone and defining adischarge passage from the combustion zone, and an outermost walldefining a dilution air passage with the outer wall to conduct air intothe discharge passage; the downstream end of the inner wall being curvedinwardly to form a forward boundary for a Coanda nozzle, and thedownstream end of the innermost wall being curved outwardly to define arear boundary for the Coanda nozzle, the Coanda nozzle encircling thedownstream end of the combustion zone between the said curved endsadapted to discharge into the recirculation passage and entraincombustion products discharged from the combustion zone into therecirculation passage; comprising a structure in which the forwardboundary of the nozzle is substantially radial, the rear boundary of thenozzle converges toward the forward boundary to define a converging airentrance to the nozzle such that a surface equidistant from the saidboundaries is directed at an angle between 15* and 20* to the forwardboundary at the nozzle outlet, and the rear boundary terminates in aguiding surface directed at a small acute angle to a perpendicular tothe adjacent forward boundary of the nozzle outlet, the guiding surfacehaving a width greater than the width of the nozzle outlet; and asupplementary outlet means from the said air passage into therecirculation passage by-passing the Coanda nozzle.
 3. A combustionapparatus comprising, in combination, an innermost wall defining acombustion zone having upstream and downstream ends, an inner walldefining an annular air passage with the innermost wall, an outer walldefininG with the inner wall an annular recirculation passage from thedownstream to the upstream end of the combustion zone and defining adischarge passage from the combustion zone, and an outermost walldefining a dilution air passage with the outer wall to conduct air intothe discharge passage; the downstream end of the inner wall being curvedinwardly to form a forward boundary for a Coanda nozzle, and thedownstream end of the innermost wall being curved outwardly to define arear boundary for the Coanda nozzle, the Coanda nozzle encircling thedownstream end of the combustion zone between the said curved endsadapted to discharge into the recirculation passage and entraincombustion products discharged from the combustion zone into therecirculation passage; comprising a structure in which the forwardboundary of the nozzle is substantially radial, the rear boundary of thenozzle converges toward the forward boundary to define a converging airentrance to the nozzle such that a surface equidistant from the saidboundaries is directed at an acute angle less than 30* to the forwardboundary at the nozzle outlet, and the rear boundary terminates in aguiding surface directed at an angle less than 10* to a perpendicular tothe adjacent forward boundary of the nozzle outlet, the guiding surfacehaving a width greater than the width of the nozzle outlet; and asupplementary outlet means from the said air passage into therecirculation passage by-passing the Coanda nozzle.
 4. A combustionapparatus comprising, in combination, an innermost wall defining acombustion zone having upstream and downstream ends, an inner walldefining an annular air passage with the innermost wall, an outer walldefining with the inner wall an annular recirculation passage from thedownstream to the upstream end of the combustion zone and defining adischarge passage from the combustion zone, and an outermost walldefining a dilution air passage with the outer wall to conduct air intothe discharge passage; the downstream end of the inner wall being curvedinwardly to form a forward boundary for a Coanda nozzle, and thedownstream end of the innermost wall being curved outwardly to define arear boundary for the Coanda nozzle, the nozzle encircling thedownstream end of the combustion zone between the said curved endsadapted to discharge into the recirculation passage and entraincombustion products discharged from the combustion zone into therecirculation passage; comprising a structure in which the forwardboundary of the nozzle is substantially radial, the rear boundary of thenozzle converges toward the forward boundary to define a converging airentrance to the nozzle such that a surface equidistant from the saidboundaries is directed at an angle between 15* and 20* to the forwardboundary at the nozzle outlet, and the rear boundary terminates in aguiding surface directed at an angle less than 10* to a perpendicular tothe adjacent forward boundary of the nozzle outlet, the guiding surfacehaving a width greater than the width of the nozzle outlet; and asupplementary outlet means from the said air passage into therecirculation passage by-passing the Coanda nozzle.